1. Field of the Invention
The present invention relates to a light emitting device including a light emitting diode (LED) chip mounted on a substrate, and a phosphor-containing transparent resin arranged in an exterior of the LED chip, and a method of manufacturing the light emitting device.
2. Description of the Related Art
There has been known a white LED light emitting device produced by a combination of an LED chip emitting excited light of a low wavelength and phosphor particles having wavelength conversion performance, in which the LED chip is mounted on a substrate attached with a reflecting plate and a transparent resin layer in which yellow phosphor particles are dispersed is coated on the LED chip (see JP-A-7-99345). However, in such a white LED light emitting device, since phosphor particles are evenly distributed, light emission color becomes more yellowish as an optical path from the LED chip through a phosphor layer becomes longer, which may result in undesired color unevenness.
As disclosed in U.S. Pat. No. 6,576,488, when a light emitting device has a structure including a uniform phosphor layer formed near an LED chip, dependency of amount of phosphor on direction is reduced, thereby decreasing color unevenness. However, in this structure, since the phosphor layer contacts the LED chip, there arises a problem in that the LED chip absorbs light emitted from the phosphor layer and the phosphor layer absorbs heat generated by the LED chip.
To overcome such problems, there has been proposed a structure in which a uniform phosphor layer is formed on a transparent resin layer and an LED chip is isolated from the phosphor layer. See, Hong Luo et al. APPLIED PHYSICS LETTER, 86, 243505 (2005), “Analysis of high-power packages for phosphor-based white-light-emitting diodes”. With this structure, the problem caused by contact between the LED chip and the phosphor may be significantly overcome.
In addition, apart from the above-described white LED structure, there has been known a white LED structure including an ultraviolet LED chip and red, green and blue color phosphors excited by light emission from the LED chip (See U.S. Patent Application Publication No. 2006/0105485). In this case, it is possible to obtain white light by forming a mixture layer of red, blue and green color phosphors on a semi-spherical transparent resin layer formed on a substrate on which the ultraviolet LED chip is mounted. However, such mixture of red, blue and green color phosphors is apt to absorb light in a low wavelength band. To overcome this, there has been proposed a method of laminating a phosphor layer emitting light having a lower wavelength to be located in an inner layer.
However, the above-mentioned multi-layered structure including the phosphor layer and the transparent resin layer requires a complicated process, and moreover, it is very difficult to form the multi-layered structure including the phosphor layer and the transparent resin layer on a flat substrate.